The present invention relates to a sensor system with monitoring device and a method for operating such a system.
Electronic stability programs of this type are systems for controlling the driving-dynamics of vehicles. These systems are primarily used to assist the driver in critical driving situations during braking, accelerating and steering, and to intervene where the driver himself/herself has no direct intervention possibility. The control system assists the driver when braking, especially on a roadway with a low or varying coefficient of friction, on which the vehicle might be no longer steerable due to locking wheels or might start to skid. It further assists in accelerating when there is a risk of spinning of the driven wheels. It can also be used to assist in steering during cornering, where the vehicle might oversteer or understeer. In total, not only the comfort but also the active safety will be improved considerably.
A control system of this type is based on a closed-loop control circuit which, during normal operation of the vehicle, takes over typical control tasks and is intended to stabilize the vehicle as quickly as possible in extreme driving situations. Sensors to sense the various driving-dynamics parameters are of special importance as generators of actual values. The precondition for a plausible control is that the sensors correctly represent the actual condition of the controlled system. This is particularly important in driving stability control operations in extreme driving situations, where a control deviation must be adjusted by the control already within a very short time. This is the reason why the ESP sensors (yaw rate sensor, transverse acceleration sensor, steering angle sensor) of an electronic stability program must be especially reliable and require constant monitoring in order to detect faults at an early point of time and rule out a faulty control which might cause a vehicle condition that is critical in terms of safety.
In view of the above, an object of the present invention is to provide a sensor system with a monitoring device and a method for operating a system of this type by which the reliability which is necessary for an electronic stability program (ESP) for vehicles can be achieved in a low-cost fashion.
This object is achieved by the present invention, wherein the sensor system includes at least two redundant sensors for sensing a process reference variable or process measured variable of a process, and the monitoring device includes a first subtractor for producing a first difference between the sensor output signals, a first and a second differentiator for the time derivative of the sensor output signals, a second subtractor for producing a second difference between the differentiated sensor output signals, and a fault analysis device by which the first and the second difference is respectively compared with a predeterminable first or second threshold value and a fault message is produced when at least one of the differences exceeds the threshold value concerned.
In a particularly favorable manner, the present invention can be combined with an ESP system for vehicles which is controlled by a microprocessor unit, and the sensor assembly is comprised of pairs of sensors in the form of respectively two redundant yaw rate sensors, two redundant transverse acceleration sensors, and/or two redundant steering angle sensors, and the monitoring device is implemented by a subprogram in the microprocessor unit.
The present invention is especially suited for the combination with a model-based monitoring of the sensors of an electronic stability program (ESP) for vehicles which is described in the parallel application (DE 199 29 155.1) and by reference herewith shall be made a part of the disclosure of this invention. In that system, respectively one of the sensors is monitored in that its output signal is compared with analytical reference values (redundancies) which are determined by means of a multi-process model from process reference variables or process measured variables that are not monitored currently. The accuracy of the calculated reference values depends, however, on the driving situation so that it cannot be excluded that specific faults will not be detected or will be detected too late in certain driving situations. The present invention offers a remedy for these cases.
A special advantage of the present invention involves that the monitoring time can be kept to be very short and the effort in time and structure can be minimized.